The present invention relates to communication apparatus in general, and more particularly to communication apparatus operative to switch dynamically communication between itself and any one of a plurality of mating communication devices of differing communication configurations.
Today, data terminal equipment (DTE), such as main frame computers, personal computers and the like, may communicate digital information amongst each other over some communication medium. Each data terminal employs data communication equipment (DCE), such as a modem, for example, to convert the digital information from the DTE into appropriate signals for transmission over the communication medium to a mating DCE and similarly to reconvert the received signals from the mating DCE back into corresponding digital information for the receiving data terminal. Modern communication equipment has become very sophisticated with the utilization of micro-computer systems which permit the equipment to be configured with a wide variety of optional features which are known as "configurables" and sometimes referred to as "straps". An example of a set of configurables is shown in Table 1 infra.
In modern modems, such as those manufactured by Codex bearing Model Nos. 2266, 2660 and 2264, for example, a prespecified portion of memory known as the active configuration memory stores binary codes representing the chosen option of each configurable. Each configurable of a given set is assigned a bit or plurality of bits of memory storage in the active configuration memory. And, the binary coding of the assigned bits represent the desired option of the configurable or strap. For example, referring to Table 1, the modulation mode may have 8 different options and therefore requires at least three bits of assignable memory storage. The assignable bits then may be coded according to the option desired. If auto V.32 is chosen as the desired option, the bits may be coded "001", for example. Note that for the configurables of low speed format, adaptive rate selection, long space disconnect, and so on have only two options and therefore require only one bit of assignable memory storage. Accordingly, the binary coding, that is "0" or "1", determines the selected option for each of these configurables. It is understood that the options of the set of configurables for the communication device are chosen so that it may be compatible in its communication configuration with the communication device it desires to mate with. Generally, a modem stores only one set of configurables in its active configuration memory which it uses to configure itself for compatible communication with a predetermined mating communication device.
At least one known modem accommodates the storage of different sets of configurables, but has only one active configuration memory for use in configuring itself. This modem is programmed to permit a manual strap change, that is, to allow the loading of another set of configurables from the stored sets of configurables into the active configuration memory by manually entering commands through a front panel. The drawback to this, of course, is that it cannot be accomplished dynamically, that is, automatically in response to some demand situation without user intervention and without the interruption of communication. User intervention for this purpose is not always convenient, because the modem may not be at the same location as the user requiring the user to go to the location of the modem which may be in another building, in some cases, to initiate manually the change in sets of configuration to permit the modem to configure itself to be compatible with another mating communication device.
The interruption of communication is especially a critical factor where a remote office, like a bank, for example, is communicating large volumes of information to a central office over a high speed leased line medium and the leased line fails for one reason or another. Modern modems have the capability of restoring communication through a backup dial line network automatically. This process is commonly referred to in the industry as "restoral". However, because the modem is restricted to only one set of configurables stored in its active configuration memory it may have to reestablish communication with the same mating communication device to retain compatibility in the communication configuration.
It is desired for some critical situations, especially for the restoral situation, that the transmitting modem be capable of switching communication dynamically to another mating communication device of a different configuration. During restoral, for example, this feature permits the modem to auto dial a predetermined modem of a central service center, for example, to apprise the center of a failure of the leased line. In addition, in a packet switching network, when the primary node is identified as malfunctioning, the modem may restore communication through a secondary or alternate node automatically without loss of communication and without human intervention. The present invention renders a communication device which overcomes the aforementioned drawbacks of present modems and provides for the above stated dynamic switching feature.